Viability of a commercial space station

[ace rooster]

Specifically with the focus on satellite assembly, repair, and service.

Missions like the Hubble repair mission are pretty much non existent at the moment, but I wonder whether this is due to them not being available. Basically, there this no way your satellite is going to get repaired if it doesn't work, so huge amounts of effort are put in to making it bomb proof. Could it be more efficient to have some infrastructure in space to permit a relaxation of these requirements? Robotics for tasks like unfolding solar panels or antenna could be entirely omitted for example, but more importantly; mountings would not need to survive launch loads if they were going to be assembled after. This is probably not much of an improvement for LEO, as everything needs to be supported somehow, but being able to shed expended* weight between LEO and GTO could be a massive saving, since it cascades back down the rocket equation.

*As in parts that have no further purpose. Structure is the main one, but vacuum seals and some thermal insulation could maybe go too, as the satellite will never be in an atmosphere again.

Another option that becomes available is orbital tugs. Ion engines are fairly heavy, so reusing one could be well worth doing. Satellites could be launched with just the fuel that the tug requires, rather than fuel and engine. That could work out lighter, even with the return trip factored in.

It would be great to think we could do everything with robotics, but currently we just cannot do better than a man with a spanner. This is why the oil industry spends tens to hundreds of millions on ships with the sole purpose of supporting just a few saturation divers.

Any thoughts on the matter? It mostly looks like a bootstrapping problem to me, where there is no market because there is no supply.

[Yora]

I think a major problem would probably access to spare parts and technical know-how for the mechanics. Even if you're dealing with a relatively small part that is broken on a sattelite, you still need to get the exact spare part and transport it from Earth to the station. If you wait until the supply rocket is fully loaded, it might take quite some time before repairs on your satelite may begin.

You also have to get each satelite from its orbit to the station and then back into its original position. Since objects at the same orbital altitude are moving at the same speed, your tug or repair ship might have to travel considerable distances to reach the satelite, which takes time and fuel. And with one station servicing the whole near-Earth space (is there a technical term for this region of space? Probably is.) that will be a lot of flying and tugging.

Eventually we'll probably see such space garages, but I won't be holding my breath to see it this century.

[Psionic Dog]

Not viable.

The spacestation would cost more than any satellite it might service, moving the station from one orbit to the next is going to be slow and/or expensive, and until orbital manufacturing takes off any replacement parts would have to be build on the ground and then intentionally launched into the wrong orbit (to the station) before being shipped to the satellite. Add in the resupply costs to keep the station flying between jobs and the very few clients that could benefit from repair over launching a newer replacement could be more cheaply serviced with either single-mission spacecraft that launch directly for the client and then return to Earth or robotic drones that can loiter for months between jobs.

As for tugs ion engines are actually rather small, and sats require some form of propulsion anyway for day to day station keeping to remain in orbit. Those tugs that have been proposed (such as the Jupiter-Exoliner proposal) usually are limited to moving dumb inert cargo such as space station supplies or reaction mass for refueling.

[Kato]

Not viable.


Pretty much. I guess the largest problem is moving stuff around in space, though. It's just not viable to either drag around the station or the satellite so they meet up. Station mainentance would also be bothersome (and I think the "right replacement parts" issue isn't that big) but just the problem of getting things moving around in space on the proper orbits will not be solved easily until we figure out new propulsion methods.

[factotum]

Yeah, I agree with the others--moving an object from one orbit to another in order to rendezvous with it for the repair job would use an enormous amount of fuel, so the station would have to be kept supplied with that from the ground. It would probably be easier to just burn the fuel getting a one-off rocket into the correct orbit to do the repair.

[halfeye]

Yeah, I agree with the others--moving an object from one orbit to another in order to rendezvous with it for the repair job would use an enormous amount of fuel, so the station would have to be kept supplied with that from the ground. It would probably be easier to just burn the fuel getting a one-off rocket into the correct orbit to do the repair.

I don't think it's a viable option at this time, but solar sails should eliminate the travel costs, though they probably wouldn't be quick.

[ace rooster]

For the servicing and repair side I was envisioning a system more parallel to the saturation diving analogy, where the station is the support vessel, but we also have a smaller diving bell. There would be a much smaller skiff able to transport technicians to and from satellites, at a lower cost than moving either the station or the satellite*. Only the most extreme failures would result in transport of a satellite, but even then you are faced with a delta v requirement in the order of 4km/s, as opposed to 9km/s+ to get a new satellite. Remember, these are the failures that the skiff is not equipped to deal with, so an earth based mission would have to be based of something big like the shuttle. It makes sense to me to keep as much of that in orbit as possible. Ease of access would become a design consideration, so these problems may even end up less than expected.

Ion engines themselves are not particularly heavy, but they rely on power supplies, and the more the better. Most satellites do not need huge solar panels, so they are dead weight once the satellite is on station. While we do need station keeping control, this is typically a couple of meters per second per day, and can be dealt with by a fairly modest drive. At that point there is no point in not having the main drive detach and do something else useful.

Any thoughts on the assembly side? How much of a saving could it be to be able to use satellites that would collapse under their own weight, and tanks that boil if exposed to air? What about bulk storage of some materials such as coolants, could it be worth transporting coolant for many satellites in one tank, to avoid having to insulate tanks against air at all?

Another thought I had was salvage. Items like solar cells can very easily outlive the satellite they are mounted on, so could probably be reclaimed. Power circuitry and communications probably could too. I would not expect this to be possible on current satellites, as they have to be built to survive a rocket launch, but if resale of components was a possibility it could be designed in.**

And that is the biggest issue I can see. There is little demand because there is no reason to design in ease of access or ease of repair, and there is no facility because there is no demand. I suppose the main question is what the satellite fleet would look like if such a facility existed. Would it look substantially different?

* The Hubble is 11 tons for reference. We probably don't want to move that in a hurry.

** You could even go so far as a standardised base, which included power, cooling, communications, and station keeping/orientation. Some 'new' satellites could be almost entirely salvaged parts, and missions with short duration could become viable due to only mission components being non-reusable.

[Ruslan]

3-D printing technology might be the answer. Imagine a roaming repair station in low Earth orbit, zipping from one broken satellite to another, replacing broken parts with locally-printed ones. Wait, you were going to say "but 3-D printers can't print electronic circuits"? Well, we'll get there soon enough.

[factotum]

For the servicing and repair side I was envisioning a system more parallel to the saturation diving analogy, where the station is the support vessel, but we also have a smaller diving bell. There would be a much smaller skiff able to transport technicians to and from satellites, at a lower cost than moving either the station or the satellite*. Only the most extreme failures would result in transport of a satellite, but even then you are faced with a delta v requirement in the order of 4km/s, as opposed to 9km/s+ to get a new satellite.

But you still have to provide the fuel for the "skiff" to achieve 8km/s of delta-V (because you want it to return to the station when it's finished its job), and that fuel has to be supplied to the station from the ground. So, not only do you have to expend lots of fuel on ground launches to put said fuel into orbit (and that's a LOT of fuel, due to the tyranny of the rocket equation), you then have all the problems associated with storing tons of rocket propellants, and believe me, those are nasty, nasty things. You can't use cryogenic ones for a situation like this because they'd evaporate within a few days, so that puts you back on ghastly stuff like UDMH and red fuming nitric acid.

Ion drives would potentially give you the required delta-V at a much less fuel cost, but at the expense of taking months or even years for the "skiff" to make its orbital change manoeuvre, which kind of defeats the point of having an orbital repair station in the first place!

[halfeye]

A station at the top of a space elevator gives you most of the advantages with a few less disadvantages. It's not going to be soon, we need a much stronger material for the tether than we yet know how to make, but given that it's a good idea.

[Kato]

3-D printing technology might be the answer. Imagine a roaming repair station in low Earth orbit, zipping from one broken satellite to another, replacing broken parts with locally-printed ones. Wait, you were going to say "but 3-D printers can't print electronic circuits"? Well, we'll get there soon enough.

Until you figure out a way to print fuel.... good luck. Also, materials to print circuits, depending on your efficiency. Honestly if that was the large issue, it would be a good idea. It isn't, though.

[weaseldust]

If you restrict yourself to the niche of geostationary satellites whose problems aren't really urgent, you'll hardly need any fuel at all. Once your repair/assembly station is in an equatorial orbit at that altitude, you can reach any other satellite in a similar orbit at very little cost. You just drop your orbit ever so little and wait to catch up, as long as you can spare a few days or weeks. But if the point is to save money on satellite assembly by having the station carry that out, you'll never need to reach the satellite really urgently anyway. Your overheads will be whatever ground control costs plus maybe a several-ton re-supply mission (food, fuel, parts, and a replacement engineer) every few months to keep the station running. That sounds like it might be sustainable to me, but it depends how much the service would be worth to the companies sending up geostationary satellites and how much the initial launch and training and so on cost.

You could possibly also put a repair/assembly station in a low 30-ish degree orbit to cater for people who are launching from the US, Japan, India, or China and who only care about their satellite being outside the atmosphere, not about having any particular orbit. As matters stand, you wouldn't be able to reach many satellites cheaply because there are infinitely many orbits at that inclination and there's not much incentive to put your satellite in a particular one, but once your station was in place, future commercial satellite launches would have an incentive to aim for your orbit, all else remaining equal. Potential future industries like space tourism and zero-g manufacturing might be customers for that kind of service.

[Ruslan]

Until you figure out a way to print fuel.... good luck.
(Resorting to snark when you have nothing of value to say is easy.) The lion share of the fuel is to actually get the station into orbit. Once you get the station into orbit, maneuvering it between different satellites doesn't require much fuel. Everything is either in low earth orbit or geosynchronous orbit. Well, I guess you need two repair stations to cover everything. Also, Ion Drive for slow orbit changes. Practically doesn't require any fuel at all.


Also, materials to print circuits, depending on your efficiency. Honestly if that was the large issue, it would be a good idea. It isn't, though.Raw materials to print new hardware are taken mostly from the old broken hardware. I thought this was obvious.

[Storm_Of_Snow]

The lion share of the fuel is to actually get the station into orbit. Once you get the station into orbit, maneuvering it between different satellites doesn't require much fuel. Everything is either in low earth orbit or geosynchronous orbit. Well, I guess you need two repair stations to cover everything. Also, Ion Drive for slow orbit changes. Practically doesn't require any fuel at all.


Personally I'd go with one station and a remote drone or two to go and collect the satellites, bring them to the station, then return them to their station once they're repaired.

But there are satellites a long way from the normal Earth orbits that might need to be serviced - Kepler (just had some problems in the last couple of weeks and in a solar orbit behind Earth and slower) and GAIA (L2) for example.



Raw materials to print new hardware are taken mostly from the old broken hardware. I thought this was obvious.
Would certainly save on costs of launch to orbit, but the crew would have to contend with residual propellant from the satellites they're breaking up (which can include some nasty chemicals), time taken to production of all but the simplest parts may be prohibitive (as for non-extrudable plastics, you're basically using vapour deposition and building the item an atomic layer at a time) and the requirements to break down and process it into raw materials (not to mention lifting the processing equipment into orbit initially) may make it too costly to be worthwhile.

If someone comes up with a Star Trek replicator that can just break items down into their component atoms and assemble new ones in a matter of seconds, sure, no problem. Without that, best bet is an annex on a space elevator where the thruster assemblies can be left in vacumn, the important bits removed and either repaired in orbit or shoved into an elevator capsule for return to earth.

[Tyndmyr]

3-D printing technology might be the answer. Imagine a roaming repair station in low Earth orbit, zipping from one broken satellite to another, replacing broken parts with locally-printed ones. Wait, you were going to say "but 3-D printers can't print electronic circuits"? Well, we'll get there soon enough.

Not really. Ignoring offgassing issues and such, you still have to lift all that mass up anyway. And also a printer now. At most, it has niche uses for parts flexibility, but it only makes the lift issue worse, not better.

[ace rooster]

But you still have to provide the fuel for the "skiff" to achieve 8km/s of delta-V (because you want it to return to the station when it's finished its job), and that fuel has to be supplied to the station from the ground. So, not only do you have to expend lots of fuel on ground launches to put said fuel into orbit (and that's a LOT of fuel, due to the tyranny of the rocket equation), you then have all the problems associated with storing tons of rocket propellants, and believe me, those are nasty, nasty things. You can't use cryogenic ones for a situation like this because they'd evaporate within a few days, so that puts you back on ghastly stuff like UDMH and red fuming nitric acid.

Ion drives would potentially give you the required delta-V at a much less fuel cost, but at the expense of taking months or even years for the "skiff" to make its orbital change manoeuvre, which kind of defeats the point of having an orbital repair station in the first place!

The 4km/s was a round trip estimate (because the moon can really help us out with changing orbits, but probably a bit optimistic), and even if it was not, the rocket equation is not entirely applicable for expected maintenance. You can send tools and a fuel stock on a much slower path using ion drives, which modifies things considerably. Ion drives are also much more effective if they can be attached to giant solar panels, which is much easier if they can be assembled rather than having to unfurl themselves. You would probably not want to use them for moving people, but parts and tools can wait.

As for the cryogenics; we are in space, so earth based constraints do not apply. Shielded from direct sunlight your cryogenic tanks could eventually freeze (take months, but still). It would actually probably be a good idea to keep the outside of the tanks below the freezing point, because they would then self seal.


One other observation is that ion drives work fine with nitrogen, and can get far greater exhaust velocities than orbital velocity. It could be possible to scoop atmosphere and use the nitrogen to maintain orbit, while holding the oxygen. The only component of fast fuel that would need lifted from earth would then be hydrogen, which is very light. It is tech that has not been developed yet, but there has been no real reason to before. You could even attempt to manufacture nitrous oxide (https://en.wikipedia.org/wiki/Nitrous_oxide#Rocket_motors) in orbit, and use mono-propellant rockets. It is not great in terms of specific impulse, but it would require no further launches for fuel. Fuel depots in various orbits could avoid some of the rocket equation issues that rapidly mount from such a low specific impulse.

Stripping down satellites is currently not feasible, but that might be because there is no consideration in the design process for it (why would there be?). If satellites were designed with the expectation that they would be stripped down in orbit at end of life, it might be very profitable. Easier to handle propellants might be used for example, with the reduced performance offset by the gains from salvage. More likely is just that the main components will be reused whole though, and nobody would go near anything dangerous except to attach connection to refill the tank.


Part of me just really wants us to be at the point where widespread commercialisation of space can take off, if we commit to the infrastructure. That infrastructure would not pay itself off for at least 30-50 years, but will probably need to be built some time. Is there anything else that we really need to be ready to start setting infrastructure up?

After that it is hopefully a case of "If you build it, they will come", and uses for microgravity and large hard vacuum will appear.

[factotum]

As for the cryogenics; we are in space, so earth based constraints do not apply. Shielded from direct sunlight your cryogenic tanks could eventually freeze (take months, but still).

Nope, not even close. Space itself might be cold enough to keep hydrogen liquid (although definitely not frozen, as you state), but the tanks for the hydrogen are attached to the space station, and no matter how much insulation you put in there will be heat flow from the main body of the station to the interior of the tanks. If it was that easy to use cryogenic fuels in space over a period of months, they'd do it, and it's notable that they don't.

As for sending tools etc. to the broken satellite via ion drive, what would be the point of that? The parts and tools are likely not the most massive part that needs to be moved--that'll be a shuttle capable of carrying people, with all the life support, food, and oxygen required to sustain them for however long it takes to move to the satellite's orbit, perform the repair, and then get back. It would also mean your satellite would be offline for however many months it took to send the parts out.

Frankly, the only point at which a commercial space station makes sense is when you have colonies in other parts of the Solar System, so the station would act as a travel hub. It would probably be higher than LEO so you don't have to keep boosting it (the ISS has to be regularly boosted due to losing orbital velocity thanks to atmospheric drag, and Skylab came down because of the same reason), too.

[Kato]

(Resorting to snark when you have nothing of value to say is easy.) The lion share of the fuel is to actually get the station into orbit. Once you get the station into orbit, maneuvering it between different satellites doesn't require much fuel. Everything is either in low earth orbit or geosynchronous orbit. Well, I guess you need two repair stations to cover everything. Also, Ion Drive for slow orbit changes. Practically doesn't require any fuel at all.

Raw materials to print new hardware are taken mostly from the old broken hardware. I thought this was obvious.

That was not meant to be snark.

I think you grossly underestimate the amount of fuel required to change into a particular orbit. This is not about turning a little to the left, it is about possible reverting your entire speed vector or turn into and orthogonal orbit to your previous one. Yeah, no single move like that is as expensive as starting but if you want to do this for a while it adds up fast.


Also, turning old circuits into the basis for new ones is an entirely different technology and I'm not quite sure how you plan to do this in a small-ish sized space station.

[ace rooster]

Nope, not even close. Space itself might be cold enough to keep hydrogen liquid (although definitely not frozen, as you state), but the tanks for the hydrogen are attached to the space station, and no matter how much insulation you put in there will be heat flow from the main body of the station to the interior of the tanks. If it was that easy to use cryogenic fuels in space over a period of months, they'd do it, and it's notable that they don't.


Cold is not the only point. Microgravity is the main point. A simple maglev system is easily strong enough to hold substantial tanks in place, which would not be possible on earth. Attachments can be entirely disconnected when not in use. While not hard it is not trivially easy, and on a conventional satellite would be just an extra failure mode. Performance is secondary to reliability for manoeuvring thrusters, which is why you commonly see monopropellants for this use. Hypergolic fuels are good for this too. Cryogenic propellants don't currently have a niche that fits them, which is why we don't see them.

The only cryogenic tank in space I can think of is the coolant tanks on IR telescopes. They last years, and they are designed to boil off.


As for sending tools etc. to the broken satellite via ion drive, what would be the point of that? The parts and tools are likely not the most massive part that needs to be moved--that'll be a shuttle capable of carrying people, with all the life support, food, and oxygen required to sustain them for however long it takes to move to the satellite's orbit, perform the repair, and then get back. It would also mean your satellite would be offline for however many months it took to send the parts out.

Routine (planned) services were what I was talking about, and many satellite networks have redundancy built in anyway. Compare the months to repair to how long it would take to get a new satellite up. The main point of the drone advanced party is the fuel dump. The rocket equation is based on taking your fuel with you, but considerable savings can be had if there is fuel half way. If you are doing that anyway it makes sense to send as much that can go that way as possible.



Frankly, the only point at which a commercial space station makes sense is when you have colonies in other parts of the Solar System, so the station would act as a travel hub. It would probably be higher than LEO so you don't have to keep boosting it (the ISS has to be regularly boosted due to losing orbital velocity thanks to atmospheric drag, and Skylab came down because of the same reason), too.

Do you think distant colonies are going to come about before we have a colony on our doorstep? Research bases maybe, but not colonies in any real sense. There are simply too many benefits to micro gravity and lack of atmosphere to skip a 'colony' there.

[Tyndmyr]

Also, turning old circuits into the basis for new ones is an entirely different technology and I'm not quite sure how you plan to do this in a small-ish sized space station.

Agreed.

For starters, yknow, things usually offgas when melted. Particularly in a vacuum. So...yeah, a lot of materials you literally can't do this with. You'd need a sealed atmo chamber, and a way to replace what's offgassed, and manage decent amounts of heat and changing atmospheric pressures. The idea that you can just generically do this for all materials without significant hardware or fuel payloads is...let's go with ridiculous.

It's not merely that printing circuits is hard. You can do that now, provided the circuit is small enough, and you can tolerate a high impedance(though this is probably a really terrible idea for a satellite), but that 3d printing is extremely poorly suited to the task at hand, and reprocessing old materials into new filament is a pretty significant thing. Generally speaking, we don't do that, here on earth, in anything smaller than a giant factory.

[wumpus]

3-D printing technology might be the answer. Imagine a roaming repair station in low Earth orbit, zipping from one broken satellite to another, replacing broken parts with locally-printed ones. Wait, you were going to say "but 3-D printers can't print electronic circuits"? Well, we'll get there soon enough.

I think ATK/Orbital has at least some sort of plan (probably just a deck of powerpoint slides right now) of building a "refueling" satellite that would "zip from one satellite to another". Understand that "zipping from one orbit to another" is supremely expensive, especially in LEO, but you could get away with some type of ion thruster (and patience. "Zip" is unlikely to be the correct term). Of course, the satellites would have to be designed to be refueled by the refueler and it isn't clear why you would want to pay for the delta-v to lift both the refueler *AND* the delta-v to get the refueler to your satellite. I'm guessing this was a job of snowballing a bunch of government types who had no clue about the delta-v requirements for attitude changes (or perhaps it was for GSO).

As far as repairing parts, I suspect that a 3d printer will be able to produce workable circuit boards (mostly slapping FPGAs and their analog counterparts) long before the robotics is capable of doing the exchange. Just look at what the astronauts had to do to fix Hubble and compare that to what robots are capable of (check some of Randal Monroe's rants about how general purpose robots are), it isn't happening any time soon.

- Note that a refueler at GSO (Geosynchronous Orbit) would make more sense as virtually all of them are on the equator and are often more valuable than the lower ones. A refueler merely needs to thrust prograde or retrograde to slow down/speed up the orbit and wait till it has moved over the part of the Earth the satellite occupies and dock with it. On the other hand, there is only room for something like 180 satellites in that peculiar orbit and it is unlikely that a significant fraction will bother with the necessary docking port (and there *still* isn't a reason to not just "bring more fuel" instead of "pay for both the fuel and the docking satellite" for the same amount of fuel).

[ace rooster]

I think ATK/Orbital has at least some sort of plan (probably just a deck of powerpoint slides right now) of building a "refueling" satellite that would "zip from one satellite to another". Understand that "zipping from one orbit to another" is supremely expensive, especially in LEO, but you could get away with some type of ion thruster (and patience. "Zip" is unlikely to be the correct term). Of course, the satellites would have to be designed to be refueled by the refueler and it isn't clear why you would want to pay for the delta-v to lift both the refueler *AND* the delta-v to get the refueler to your satellite. I'm guessing this was a job of snowballing a bunch of government types who had no clue about the delta-v requirements for attitude changes (or perhaps it was for GSO).


Rockets have a fixed payload that they can get to orbit, and you can't make any real savings by not firing a full payload. One advantage of that type of satellite is being able to fill out extra space in launches. It would be competing with mircosatellites for the space, but that space could be considerably cheaper than just sending extra fuel initially, especially if that makes the satellite too heavy for the launch that was intended. I agree that it is still probably not a particularly effective idea, because it can only deal with one failure mode, but it might have a niche.

Ion thrusters can do considerably better than you might expect, if you have enough power. A spacecraft with only solar panels and an ion thruster could accelerate at up to 1km/s per day if you set it up right (not sure if we have an engine light enough, but certainly within the realm of MHD engines). You would probably want to use a higher exhaust velocity than the 20km/s that uses, but they are really not as sluggish as generally assumed. They are generally constrained by power available, and in no rush, so they work as fast as they can with the power available.

[Storm_Of_Snow]

I think ATK/Orbital has at least some sort of plan (probably just a deck of powerpoint slides right now) of building a "refueling" satellite that would "zip from one satellite to another". Understand that "zipping from one orbit to another" is supremely expensive, especially in LEO, but you could get away with some type of ion thruster (and patience. "Zip" is unlikely to be the correct term). Of course, the satellites would have to be designed to be refueled by the refueler and it isn't clear why you would want to pay for the delta-v to lift both the refueler *AND* the delta-v to get the refueler to your satellite. I'm guessing this was a job of snowballing a bunch of government types who had no clue about the delta-v requirements for attitude changes (or perhaps it was for GSO).

The main issue with lifespans of satellites is how long the power systems, electronics and control systems will last (especially the gyroscopes), fuel is relatively inexpensive in terms of both cost and mass to lift in comparison.

If it does get to the point where a recovery station is viable, my guess would be we'd see more modular systems - a mission pallet attached to an attitude control component and plug in modules for whatever power source the mission needs, with the mission pallet being pretty much all that's launched into orbit (unless there's the need for something really specific), and the rest being recycled from satellites that have been end-of-lifed, recovered, the old mission pallet removed and the new one swapped in.



As far as repairing parts, I suspect that a 3d printer will be able to produce workable circuit boards (mostly slapping FPGAs and their analog counterparts) long before the robotics is capable of doing the exchange.

We can probably do it now - the main issues are cost of production and the time it would take.



Just look at what the astronauts had to do to fix Hubble and compare that to what robots are capable of (check some of Randal Monroe's rants about how general purpose robots are), it isn't happening any time soon.

Agreed - a telepresence system might be viable (possibly the only solution for some satellites that need specialised repairs), but comms lag may be an issue, especially if the repair is on something not in a standard Earth orbit.



- Note that a refueler at GSO (Geosynchronous Orbit) would make more sense as virtually all of them are on the equator and are often more valuable than the lower ones. A refueler merely needs to thrust prograde or retrograde to slow down/speed up the orbit and wait till it has moved over the part of the Earth the satellite occupies and dock with it. On the other hand, there is only room for something like 180 satellites in that peculiar orbit and it is unlikely that a significant fraction will bother with the necessary docking port (and there *still* isn't a reason to not just "bring more fuel" instead of "pay for both the fuel and the docking satellite" for the same amount of fuel).

I'd actually say a polar orbit, especially if you're using remote/autonomous drones to retrieve, as sooner or later you'll be going fairly close to the item you want to snag.

One issue with this that I havn't seen mentioned yet - what about military sats? I can't see any government being too happy about people they have no control over being anywhere near their equipment, and each nation having their own crews up there could get messy.

[Rakaydos]

I'd actually say a polar orbit, especially if you're using remote/autonomous drones to retrieve, as sooner or later you'll be going fairly close to the item you want to snag.

Which polar orbit? there's literally an infinite number of them.

Geosynchronus orbit, at least, is a single specific orbit with properties that make it valuable. Being on a near-geosynch orbit, you'll lazilly drift past all of them, a short jaunt away.

Ion isnt the best option, actually- Electrotether is. It's a long wire that effectively pushes off the earth's magnetic field for thrust, without using propellant, just energy, the same way a propeller pushes off water.

The biggest problem, though, is that all the existing satelites simply arnt designed for servicing.